Medical ventilator systems have been long used to provide supplemental oxygen support to patients. These ventilators typically comprise a source of pressurized oxygen which is fluidly connected to the patient through a conduit. Some ventilator systems monitor the patient during ventilation. In some systems, the pulse arterial oxygen saturation (SpO2) is monitored via a pulse oximeter attached to the patient.
A pulse oximeter includes a light sensor that is placed at a site on a patient, usually a fingertip, toe, forehead or earlobe, or in the case of a neonate, across a foot. Light, which may be produced by a light source integrated into the pulse oximeter, containing both red and infrared wavelengths is directed onto the skin of the patient and the light that passes through the skin is detected by the sensor. The intensity of light in each wavelength is measured by the sensor over time. The graph of light intensity versus time is referred to as the photoplethysmogram (PPG) or, more commonly, simply as the “pleth.” From the waveform of the PPG, it is possible to identify the pulse rate of the patient and when each individual pulse occurs. In addition, by comparing the intensities of two wavelengths when a pulse occurs, it is possible to determine blood oxygen saturation of hemoglobin in arterial blood. This relies on the observation that highly oxygenated blood will relatively absorb more red light and less infrared light than blood with a lower oxygen saturation.
Some of previously known medical ventilators attempt to automate the adjustment of fractional inspired oxygen (FiO2) as a function of the patient's SpO2. While these previously known automated ventilation systems utilize the oximeter readings for improving ventilation, patient care could be improved by further coordinating the operation of the two devices, particularly by integrating the analysis, storage and display of particular aspects of oximeter data and respiratory data.